1. Field of the Invention
This invention relates to crosslinked polymers of maleic anhydride and alkyl vinyl ethers, and, more particularly to a process for hydrolyzing and neutralizing such polymers substantially instantly at room temperature.
2. Description of the Prior Art
Crosslinked and polymers of maleic anhydride and a C.sub.1 -C.sub.5 alkyl vinyl ether, e.g. methyl vinyl ether, and, optionally, a hydrophobic monomer, are useful thickener and emulsion stabilizers. However, these polymers must undergo hydrolysis before thickening and gelation can occur to form a clear or translucent, viscous gel in water. Kwak et al U.S. Pat. No. 5,178,143. Usually the polymer resin is supplied to the user as a hydrophobic powder designed to wet easily. As a powder the resin is in its anhydride form. Hydrolysis converts the anhydride group to the diacid which causes the polymer to begin to uncoil. The hydrolysis process requires (a) dispersing the polymer in water at room temperature for 24-48 hours; (b) by heating the polymer in water at 65.degree.-80.degree. C. for 30-90 minutes; or (c) heating the polymer in dilute sodium hydroxide solution at 65.degree. for 30 minutes.
When base is added to the hydrolyzed (diacid) form of the resin, the base is consumed and the crosslinked polymer structure expands until the diacid is fully neutralized. High viscosity gels can be formed at or near full neutralization in the pH range of 5.5-8.5. The gel viscosity is lower for only partially neutralized crosslinked polymers, and for gel solutions having excess base which acts like a salt to reduce charge interaction on the polyelectrolyte causing the polymer to begin to coil.
Accordingly, it is an object of this invention to provide a process for preparing hydrolyzed, suitably neutralized gel solutions of crosslinked polymers of maleic anhydride and a C.sub.1 -C.sub.5 alkyl vinyl ether substantially instantaneously (less than 1 minute) at room temperature (about 20.degree. C.) to form a clear gel solution at a pH of 5-12, having a Brookfield viscosity of at least 20,000 cps.
A specific object of the invention is to provide a process for hydrolyzing and neutralizing polymers of crosslinked maleic anhydride and methyl vinyl ether in a base substantially instantaneously at room temperature.